Oxidation mechanisms of ammonia and ethanol mixed fuel by using the ReaxFF-MD simulation

ReaxFF molecular dynamics simulations were employed to investigate the behavior of ammonia and ethanol mixed fuel in different conditions, focusing on their combustion reaction mechanisms, intermediates, free radicals, and final product formation at different equivalence ratios. The results reveal that ammonia is primarily consumed by OH free radicals, leading to the formation of the NH₂ free radical. NH₂ radical undergoes further transformations, forming H₂NO, H₃NO, HNO, HO₂, NO, NO₂, HONO, and NH free radicals. The CH₃, an intermediate of ethanol, influences the abundance of other free radicals such as H and OH, which also leads to a significant increase in CH₂O. In oxygen-rich conditions, OH, HO₂, and H₂O₂ demonstrate higher concentrations compared to oxygen-poor conditions. The NO_x species include NO, NO₂, and NO₃ in rich- and stoichiometric-oxygen conditions, whereas in oxygen-poor conditions, only NO is formed. The number of H₂O decreases as the proportion of ethanol decreases due to the lack of O atoms, and the amount of H₂ continues to increase in the oxygen-poor system. The limited availability of oxygen alters the reaction mechanism, reducing the occurrence of primary form reactions of H₂O with the assistance of O, OH, and HO₂. Instead, an increasing number of branching chain reactions become prominent at high temperature, leading to the formation of a significant amount of H₂.